The 5.6 magnitude quake struck at 4:31 a.m. local time, causing walls to collapse and chimneys to topple in the city of Pernik.
Hospitals there reported about 30 people sought medical help following the pre-dawn tremor, mainly complaining of high wblood pressure.
The shaking was strong enough to prompt many residents in Sofia to flee their homes and gather in the streets as frightening aftershocks rumbled across the region for several hours.
The U.S. Geological Survey determined the initial quake was centered about 14 miles west of Sofia and occurred at a relatively shallow depth of 5.8 miles.
On September 30, 1858, when the future Bulgarian capital was still only a provincial town in the Ottoman Empire, it was hit by a tremor estimated to have been between magnitude 6.6 and 7.0.
Nearly 80 percent of the buildings were damaged by that shaking, including 19 of the city’s 29 mosques that saw their minarets collapse.
Four people died in that quake, which also caused huge cracks to appear in the ground outside of town.